Abstract: Cadmium (Cd) is a non-essential trace element for organism, and has strong toxicity at low concentrations. In recent years, cadmium in aquatic animals is excessive because of industrial pollution and the use of aquatic animals or their scraps as feed. Cadmium has a long residual time, and can be bioaccumulated through the food chain transfer, which is becoming a threat to the human health. An overview of pollution sources, the speciation, the different speciation hazards and detection methods about cadmium are described.